Replace the trailing arm bushings now so you don't have to drop subframe again for a while. Might as well replace the rear Z links and stabilizer mounts too. How old is the differential mount? If you can't get all of that now at least do the trailing arm bushings. The other stuff is fairly easy to get to.

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If it ain't broke take it apart and find out why.

1983 300SD, 4 speed
1994 C280
1987 300TD wagon
1996 HD Road King

Ride in Peace Eric Peterson, Harley of Macon